This invention relates to a process for producing a maltooligosaccharide derivative very useful, for example, as a precursor of a modified oligosaccharide derivative having one or more modifying groups at the 6-position or the 4- and 6-positions of the non-reducing-end glucose residue, and having or not having an optically measurable group at the reducing end, said modified oligosaccharide derivative being effectively usable as a substrate for determining .alpha.-amylase activity, or an intermediate of the substrate; and a process for producing the substrate for determining .alpha.-amylase activity, by use of said maltooligosaccharide derivative.
Determination of .alpha.-amylase activity in samples, in particular, saliva, sancreatic juice, blood and urine in a human body gives an important indication for medical diagnoses. For example, in the case of pancreatisis, pancreas cancer and parotiditis, the level of .alpha.-amylase activity in blood and urine is much higher than its usual level. For the determination, there has come to be generally employed in recent years a coupling enzyme method using as substrate a maltooligosaccharide having a color-producing group at the reducing end and a non-reducing end glucose residue modified at the 6-position or the 4- and 6-positions.
In the synthesis of such a substrate having a non-reducing end glucose residue modified only at the 6-position or the 4- and 6-positions, if there is a common intermediate which permits free and easy introduction of various modifying groups only into the 6-position or the 4- and 6-positions of the non-reducing end glucose residue, it becomes possible to synthesize rapidly and efficiently a substrate for determining .alpha.-amylase activity or an intermediate thereof, which has higher performance characteristics and a newer function. Therefore, the production and development of a substrate for determining .alpha.-amylase activity proceed rapidly, and hence the common intermediate is of high utility value.
Japanese Patent Unexamined Publication Nos. 60-54395 (U.S. Pat. Nos. 4,709,020 and 4,818,692) and 2-49796 (U.S. Pat. No. 5,011,923) disclose a polyacetylmaltooligosaccharide derivative retaining the hydroxyl groups at the 4- and 6-positions of the non-reducing end glucose residue, and a process for producing the same. Utilization of these intermediates permits selective and easy synthesis of a substrate having a non-reducing end glucose residue modified only in the hydroxyl group at the 6-position and a substrate having a non-reducing end glucose residue modified at the 4- and 6-positions with bridge type blocking groups.
However, the synthetic process of the polyacetylmaltooligosaccharide derivative retaining the hydroxyl groups at the 4- and 6-positions of the non-reducing end glucose residue which has been disclosed in the above-mentioned Japanese Patent Unexamined Publication Nos. 60-54395 and 2-49796, has the following defect. The synthetic process uses a commercially available oligosaccharide derivative as a starting material and comprises three independent steps, i.e., a step of blocking the 4- and 6-positions, an acylation step and a deblocking step. Moreover, as a blocking group for the 4- and 6-positions, there is used a cyclic ketal (or acetal) type blocking group such as ethylidene group, isopropylidene group, benzylidene group or the like. Therefore, both the blocking step and the deblocking step require severe conditions and a troublesome procedure, so that the kind of the color-producing group at the reducing end is unavoidably limited.
Accordingly, there has been an eager desire for the advent of a process for producing a polyacrylmaltooligosaccharide derivative retaining the hydroxyl groups at the 4- and 6-positions of the non-reducing end glucose residue, easily in high yield under mild conditions by using a commercially available oligosaccharide derivative as a starting material.